As component corrosion becomes an increasingly important consideration in lifetime reliability, it also becomes more important to be able to predict and measure that corrosion. For example, there are strong incentives to increase nuclear fuel element linear heat ratings, coolant temperatures, and/or in-reactor residence times. Consequently, there is a growing need to be able to understand and characterize zircaloy cladding corrosion as well as to monitor corrosion. The traditional approach used to characterize corrosion behavior is to use discrete data obtained by periodically weighing test specimens. This requires non-productive shutdown of the test facility and lost time while the measurement is made. Furthermore, it is virtually impossible to characterize instanteous corrosion rates with discrete data, particularly through transition regions where rates may change dramatically over short periods of time.
A number of different techniques have been developed in measuring the effects of corrosion. For example, U.S. Pat. No. 3,253,219 (Littler) discloses a method of determining corrosion rate using the change in the output frequency of a piezoelectric crystal to which a corrodible specimen is attached. A further type of corrosion-measuring device is disclosed in U.S. Pat. No. 3,056,284 (Marsh et al) which determines the coating of a foreign material on, or the loss of exposed surface from, a test or reflectance element, and which employs an elongate body having at least two pairs of reflecting surfaces. An ultrasonic wave of a selected frequency is applied to the body and multiple reflections are produced. The applied frequency is adjusted to provide a condition of internally reflected resonance. Further, U.S. Pat. No. 3,104,355 (Holmes et al) discloses a corrosion measuring probe with a temperature compensating element connected in a Wheatstone bridge. Other general measurement techniques of possible interest here include those disclosed in U.S. Pat. No. 2,280,226 (Firestone) which relates to a flaw detecting device in which high frequency vibrations are transmitted into a part to be inspected for flaws and the intervals of direct and reflected vibrations are determined; U.S. Pat. No. 3,004,425 (Henry) which discloses the use of a piezoelectric transducer in combination with ultrasonic pulse echo techniques to provide inspection of a test specimen close to the entrant surface; and U.S. Pat. No. 3,587,299 (Taley) which discloses a char rate detector employing an ultrasonic sound generator and sound wave reflectors embedded at predetermined depths between two opposing surfaces of virgin ablative material.